Patent Document 1 describes fluoroethercarboxylic acids obtainable by allowing an alcohol to add to a perfluoro(vinyl ether) and reducing the compound obtained.
Patent Document 2 describes fluoroethercarboxylic acid salts obtainable by utilizing the ring-opening reaction of tetrafluorooxetane.    [Patent Document 1] United States Patent Application Publication 2007/0015864    [Patent Document 2] International Publication 2005/003075